Electrolytic process for the manufacture of azo compounds

ABSTRACT

A PROCESS IS PROVIDED FOR THE MANUFACTURE OF AZO COMPOUNDS BY THE ELECTROLYTIC OXIDATION OF HYDRAZO COMPOUNDS IN AN ALKALI METAL HALIDE ELECTROLYTE.

l. A. PRAGER ELECTROLYTIC PROCESS FOR THE MANUFACTURE OF AZO COMPOUNDS March 14, 1972 Filed April 9, 1969 INVENTOR. IRWIN ,4. PRAGER MW ficgdm ATTURNEXS' nited States Patent 3,649,484 E TROLYTIC PROCESS FOR THE MANU- EL FACTURE 0F AZO COMPOUNDS Irwin A. Prager, Naugatuck, Conn., ass gnor to Uniroyal, Inc., New York, N.Y. Filed Apr. 9, 1969, Ser. No. 814,734 Int. Cl. C011) 29/06; C07c 107/02 US. Cl. 20479 Claims ABSTRACT OF THE DISCLOSURE A process is provided for the manufacture of azo compounds by the electrolytic oxidation of hydrazo compounds in an alkali metal halide electrolyte.

This invention relates to a process for the manufacture of azo compounds from hydroza comp 111 P ticular, to a process for the manufacture of azodlcarbonamide from hydrazodicarbonamide.

The compound, azodicarbonamide, is particularly effective as a blowing agent in the manufacture of cellular products of low density, such as foam plastics, squong es, and the like. The compound provides upon decomposition a gaseous product, e.g. nitrogen, in a relatively large volume, which is released in situ under certain condltlons when the compound is mixed with the material to be foamed, such as rubber, plastics, and certain elastomeric materials. Foam materials, especially plastic foams, have wide utility in thermal insulation, buoyant material for life jackets or surfboards, seat cushions, packaging material and a host of other uses too numerous to mention.

Azodicarbonamide evolves into a gas when heated to about 160 C. to 220 C. This compound is known in the trade under several designations, such as Kempore, Celogen AZ, and Porofor '505A.

It is known to produce azo compounds by the chemical oxidation of hydrazo compounds. Such methods include the oxidation of the hydrazo compound using chlorine or an organic or inorganic compound which is added to initiate and maintain the oxidation. One method proposed uses a sulfuric acid solution of potassium dichromate or potassium permanganate. As these reagents in the foregoing method are rather diflicult to handle and tend to be expensive, the conversion process based on the use of such reagents likewise tends to be expensive. Moreover, some of the chemical oxidizing agents are potentially explosive and/or toxic. As illustrative of procedures which have been employed using chemical reagents as oxidants, reference is made to US. Pats. No. 2,988,545, No. 3,017,406, No. 3,192,196 and No. 3,227,706.

It is an object of this invention to provide a safe and simple method for oxidizing hydrazo compounds without using a chemical oxidizing agent.

Another object is to provide an electrolytic process for oxidizing hydrazo compounds, for example, oxidize hydrazodicarbonamide to azodicarbonamide.

A still further object is to provide an electrolytic process for producing azodicarbonamide with high yields.

These and other objects will more clearly appear from the following description and the accompanying drawing, wherein the figure shows diagrammatically one embodiment of an electrolytic cell which may be employed in carrying out the invention.

Stating it broadly, the novel process of the invention may be employed in oxidizing hydrazo compounds of the yp "ice to the corresponding azo compounds of the type RCN=N-CR 11 l where both constituents R are the same and where R may be selected from the group conslstlng of OR and R being selected from the group consisting of alkyl groups containing from 1 to 18 carbon atoms and cycloalkyl groups containing from 4 to 7 carbon atoms and each of R and R being selected from the group consisting of hydrogen, 'alkyl groups containing from 1 to 18 carbon atoms, cycloalkyl groups containing from 4 to 7 carbon atoms, unsubstituted aryl groups, such as phenyl, naphthyl, and aralkyl groups containing a total of 7 to 18 carbon atoms. An aralkyl group would include a radical consisting of a phenyl group and an alkyl group in which the linkage between the aralkyl group and nitrogen may be one of the carbon atoms in the phenyl group or the alkyl group. Benzyl and tolyl are examples of aralkyl groups.

Thus, the group OR may be an ethoxyl (OC H a methoxyl (OCH3), or other alkoxyls. The com pound can be treated to produce the azo compound which is known as ethyl azodicarbonic e-ster.

A specific hydrazo compound with which the invention is particularly concerned is hydrazodicarbonamide known by the formula Specific examples of other hydrazo compounds which may be treated in accordance with the invention are hydrazo bisformamides, such as 1,6-di-n-dodecyl hydrazo bisformamide, 1,6-dicyclohexyl hydrazo bisformide, etc.; compounds where :R and R are the same, such as 1,1,6,6- tetramethyl hydrazo bisformamide; and such other compounds as esters of hydrazo diformic acid, e.g. di-n-amyl ester, and the like.

An advantage of the process is that useful lay-products may be produced depending upon the type of electrolyte employed in carrying out the reaction.

As stated hereinbefore, chemical oxidizing agents are not added to promote the reaction. In essence, the hydrazo compound is dispersed in a compatible electrolyte, which may be a solution of alkali metal halide, such as sodium chloride or sodium bromide, and the hydrazo compound oxidized electrolytically at the anode side of the electrolytic cell. The useful by-product which is formed with the foregoing electrolyte is sodium hydroxide and gaseous hydrogen which can be easily recovered, together with high quality azodicarbonamide at high yields and low cost. All that is required is electrical energy to effect primary oxidation of the dispersed compound.

The oxidation is carried out in a typical electrolytic cell system, having preferably anode and cathode compartments separated by a semi-permeable membrane, such as asbestos, sintered glass, ceramic, portland cement, and the like. The purpose of the membrane is to keep the products which are generated at each of the electrodes from reacting with each other while, at the same time, allowing current to flow through the cells with minimum resistance. The electrodes for both compartments may be made of graphite, platinum or other corrosion resistant materials.

As illustrative of the type of cell which may be em ployed in carrying out the process of the invention, reference is made to the accompanying drawing which shows a cell comprised of a container 10, for example, acrylic plastic divided into two compartments by a permeable membrane or diaphragm 13 formed of suitable material, such as asbestos. A negative electrode 11 of graphite is suspended in cathode compartment 14, and a positive electrode 12, also of graphite, is suspended in anode compartment 15, the anode compartment having a stirrer 16 for maintaining the hydrazo compound uniformly dispersed throughout the compartment during application of an anodizing current.

Generally speaking, a procedure which may be employed is to add two equal volumes of an electrolyte solution to each half-cell of the electrolytic cell. Hydrazodicarbonamide is added to the anode compartment only. After immersing the electrodes in the solution, the power is turned on. During the reaction, azodicarbonamide and acid are formed in the anode compartment while caustic soda and gaseous hydrogen are formed in the cathode compartment. The reaction is terminated when the required electrochemical equivalents, according to Faradays law, are consumed. In actual practice, a slight excess current is used since current efiiciency is not quite 100 percent. The temperature at which the oxidation is carried out is not critical and may range between room temperature and 60 C., and preferably from about 25 to 46 C. Thirty ampere-hours at a voltage of 25 EMF have been found satisfactory.

As illustrative of the invention, the following examples are given:

EXAMPLE 1 A cell in accordance with that illustrated in the drawing was prepared by adding 200 grams of sodium bromide and 2000 cc. of Water in each of the compartments. The stirrer was turned on to agitate the anode electrolyte and, at the same time, 59 grams (0.5 mole) of hydrazodicarbonamide was added to the compartment. The pH of the This example is similar to Example 1 except that the electrolyte is sodium chloride with a low concentration of bromide.

Into each half-cell of the same electrolytic cell were added 200 grams of sodium chloride, 12 grams of sodium bromide and 2000 cc. of cold water. To the anode compartment was added 59 grams (0.5 mole) of hydrazocarbonamide and the solution subjected to stirring. The pH of the solution was approximately 7. The power was then applied and the current flow adjusted to 10 amperes. After 3 hours or a total consumption of 30 ampere-hours, the oxidation treatment was terminated. The anode solution was removed and filtered to separate the product which was then washed and dried. The azodicarbonamide mod not obtained weighed 53 grams which calculated to a yield of 91.3

EXAMPLE 3 This example illustrates the use of sodium bromide with the electrolyte in the anode compartment maintained at a low pH. Into each half-cell of the same electrolytic cell were added 200 grams of sodium bromide and 2000 cc. of Water. To the anode compartment was added 59 grams (0.5 mole) of hydrazodicarbonamide and 10 cc. of concentrated (36% to 37%) hydrochloric acid, the solution meanwhile being stirred. Ten cubic centimeters of 50% sodium hydroxide were also added to the cathode compartment. The pH of the solution in the anode compartment was approximately 1 to 2 (pH paper) and, in the cathode compartment, approximately 11 to 14. After 5.5 hours of an average current flow of about 5.8 amperes or 31.9 ampere-hours, the oxidation treatment was terminated. On filtering, washing and drying, 56 grams of azodicarbonamide were obtained which calculated to a yield of about 96.7%.

EXAMPLE 4 This example demonstrates the use of sodium chloride as the electrolyte which is maintained at a low pH.

Into each half-cell of the electrolytic cell described hereinabove were added 200 grams of sodium chloride and 2000 cc. of cold water. To the anode compartment were added 50 cc. of concentrated hydrochloric acid (36% to 37%) and 59 grams (0.5 mole) of hydrazodicarbonamide while the solution was being stirred. The pH of the medium was approximately 1 to 2. The power was then applied and adjusted to 10 amperes. After 3 hours or the consumption of 30 ampere-hours, the oxidation treatment was terminated. On filtering, washing and drying, a 72.3% yield of azodicarbonamide was obtained.

As will be appreciated, by employing conditions similar to those of Examples 1 to 4, azo compounds can be produced from a large variety of hydrazo compounds of the type listed herein. The electrolyte employed should be compatible with the compounds being treated. Electrolytes useful in this regard include those based on a halide selected from the group consisting of chlorides and bromides. Thus, the halide may be hydrochloric or hydrobromic acid, or salts, such as chlorides and bromides of sodium, potassium, calcium, zinc, and the like; or electrically conductive electrolytes of organic chlorides and bromides. I have found it particularly advantageous to employ electrolytes based on chlorides and/or bromides of sodium and/or potassium.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What is claimed is:

1. A process for producing an azo compound which comprises providing an electrolytic cell divided into anode and cathode compartments by a semi-permeable membrane and containing an electrolyte based on a compound selected from the group consisting of alkali metal chlorides and bromides, dispersing an hydrazo compound of the formula anode compartment to the corresponding azo compound having the formula wherein R in each formula is the same and wherein R is selected from the group consisting of --OR and R being selected from the class consisting of alkyl groups containing 1 to 18 carbon atoms and cycloalkyl groups containing 4 to 7 carbon atoms, and each of R and R being selected from the class consisting of hydrogen, alkyl groups containing from 1 to 18 carbon atoms, cycloalkyl groups containing from 4 to 7 carbon atoms, unsubstituted aryl radicals selected from the group consisting of phenyl and naphthyl radicals, and aralkyl groups selected from the group consisting of benzyl and tolyl radicals,

2. The process of claim 1, wherein the electrolyte is based on a compound selected from the group consisting of chloride and bromides of sodium and potassium.

3. The process of claim 2, wherein the hydrazo compound dispersed in the electrolyte is hydrazodicarbonamide and wherein the oxidized product thereof is azodicarbonamide.

4. The process of claim 1, wherein the semi-permeable membrane is selected from the group consisting of asbestos, ceramic, sintered glass and portland cement.

5. The process of claim 1, wherein the electrolytic oxidation of the compunds is carried out at a temperature of about room temperature to C.

References Cited UNITED STATES PATENTS 1,397,239 11/1921 Slater 204 1,599,108 9/1926 Wilson 204-128 3,190,873 6/1965 Porter et al. 260192 3,214,362 10/1965 Juda 20498 XR 3,225,026 12/1965 Huibers 260-192 3,242,059 3/1966 Cottam et a1. 20498 3,522,233 7/1970 Sheppard et a]. 2607192 FOREIGN PATENTS 1,059,892 6/1959 Germany 20479 FREDERICK C. EDMUNDSON, Primary Examiner US. Cl. X.R. 260192 

